What you’re getting yourself into

Key Points

Blood flow restriction (BFR) training involves cutting off venous blood flow out of a limb, but still allowing arterial blood flow into a limb, resulting in the best pump of your life.

Because of the massive pump you get from BFR training, people assume it’s the bee’s knees for hypertrophy. However, thus far, it doesn’t seem to cause any more growth than conventional, heavy training.

The biggest benefit of BFR training actually seems to be notable increases in strength when it’s added to heavy training. It causes a high degree of muscle activation (rivaling heavy lifting) and causes virtually no muscle damage, making it essentially “free” volume to help you get stronger without compromising recovery.

There are a few more cool benefits, including enhancing recovery from training, and reducing atrophy when you’re injured.

Blood flow restriction (BFR) training, or occlusion training, is something that’s met with mixed reactions. Some people are fully aboard the BFR bandwagon, and others think it’s just a gimmick.

To this point, the available evidence suggests that BFR training is quite effective as an adjuvant to conventional, heavy training … just not for the reasons most people think.

So first off, what is BFR training?

Essentially, you use a knee wrap or an elastic band to cut off venous blood flow in your arms or legs. The blood pressure in your veins (which remove blood from the limb) is substantially lower than the blood pressure in your arteries (which bring blood to the limb), so you apply the wrap tight enough to keep blood from leaving the limb, while still allowing blood to enter the limb.

Most of the original studies used a special cuff to occlude venous blood flow, but using knee wraps or an elastic band works just as well. From a scale of 0 (meaning no pressure at all) to 10 (meaning the pressure you’d expect form a tourniquet before getting a limb amputated), the pressure on your arms should feel like a 7, and the pressure on your legs should feel like an 8 or 9. Apply the wrap or band as close to the top of the limb as possible – very close to the groin if occluding venous blood flow from the legs, and very close to the arm pit if occluding venous blood flow from the arms.

Use a light load. It should be a weight you can get for 30-40 reps when you’re fresh (~20-30% of your 1rm is what’s used most often in the research). Pump out as many reps as you can, rest for about 30 seconds, and pump out some more reps. 3-4 sets with short rest, totaling 60-100 reps is what’s done most often in the literature. In some of the studies, the wraps are removed between sets, and in some, they’re left on between sets (bro-tip: it’s much more convenient to just leave them on between sets and admire all of your bulging blood vessels).

While you’re pumping out all of these reps, a ton of blood is driven into the limb, and very little of it can leave. The result: the best pump you’ve ever experienced.

When people try it for the first time, they assume that it must be god’s gift to hypertrophy training. That’s what most people use it for – to get jacked. However, it has other uses that go far beyond hypertrophy and, arguably, hypertrophy isn’t even the biggest benefit you can get from BFR.

But, before we get into the effects of BFR training, let’s backtrack a bit, and take a look at why and how it works.

The Mechanisms of BFR Training

There are six major mechanistic reasons why BFR training works for building muscle and strength.

Metabolic Stress. Identified as one of the three primary mechanisms of muscle hypertrophy (along with muscular tension and muscle damage), metabolic stress signals muscles to grow. Constant BFR (leaving the wraps on between sets) works better that intermittent BFR (taking the wraps off between sets) for this purpose. Intermittent BFR leads to greater metabolic stress than regular low-load training, and constant BFR leads to similar levels of metabolic stress as training at 65% of your 1rm without BFR – equal metabolic stress with much lower loads.

Motor Unit Recruitment (one, two, three). Regular low-load training potentially doesn’t recruit as many motor units as heavier training, even when training to failure. I say “potentially” because you assess motor unit recruitment via EMG, and it’s very possible that as the first motor units recruited start to fatigue, they “drop out,” so that the EMG readings at failure would be lower than they would have been when training with heavier loads (which wouldn’t give motor units enough time to fatigue and “drop out”), even if motor unit recruitment throughout the entirety of the set was identical (more on that here). Regardless, research shows that motor unit recruitment is substantially higher with low-load BFR training (specifically constant BFR) than with low-load training without BFR, and that motor unit recruitment is similar for low-load BFR training and heavier, conventional training without BFR. This, as we’ll see later, is probably the biggest benefit of BFR training.

Cellular Swelling. Similar to metabolic stress, cell swelling has been identified as a mechanism that can cause hypertrophy. Muscle thickness increases roughly 11.5-12% directly after a BFR workout, due to the increased fluid in the muscle, indicating (to use a scientific term) a buttload of cellular swelling.

Modulating Hypertrophy Signalling Pathways and Gene Expression (one, two, three). Key signaling pathways (like the mTOR pathway) and genes (like the myostatin gene) are affected to a greater degree by low-load BFR training than low-load training without BFR. BFR training and heavier, conventional training affect them similarly, increasing protein synthesis and decreasing myostatin to similar degrees. There’s also some data suggesting BFR increases the activity of heat shock proteins which may decrease catabolic signaling, but as far as I know, that’s only been observed in one rodent study thus far.

Satellite cell proliferation and myonuclear addition. If you remember from a previous article (I’m overhauling this one in the future because there are some things about it I’m not too pleased with as-is, but the mechanistic stuff about satellite cells and myonuclei is solid), addition of new myonuclei is an absolutely essential factor for long-term hypertrophy. Muscles can grow until the muscle fibers hit their myonuclear domain limit without adding more myonuclei, but to continue growing, the addition of new myonuclei from satellite cells is crucial. Low-load BFR training increases the satellite cell pool and causes myonuclear addition much more effectively than low-load training without BFR, and to a similar degree as heavier, conventional training.

Growth Hormone Release. It’s not clear whether acute elevations in ostensibly anabolic hormones affect muscle growth in any meaningful way, but the results of this study were eye-catching enough to at least give it a mention. Low-load BFR training to failure caused an increase in growth hormone 290x higher than resting levels, and approximately 4x higher than low-load training to failure without BFR.

Mechanisms are cool and all, but what are the effects on strength and hypertrophy?

For starters, overall, low-intensity BFR training seems to be about as good for hypertrophy and strength as heavier conventional training. Kreiger found an effect size of .35 for hypertrophy and an effect size of 0.8 for strength from multi-set conventional resistance training in his meta-analysis, and Loenneke found an effect size of .39 for hypertrophy and an effect size of .58 for strength from low-intensity BFR training in his. However, it’s worth pointing out that the overall effect sizes for both hypertrophy and strength are depressed quite a bit in the low-intensity BFR training meta-analysis, since it included studies where the mode of exercise was incline treadmill walking with BFR. When only looking at resistance training studies, the effect size was 1.08 for both strength and hypertrophy (though, obviously, with a smaller sample size).

When taking an aerial view, BFR training and conventional training have pretty similar effects. The fact that you get similar hypertrophy from low-load BFR training isn’t overly surprising, in light of the fact that number of hard sets is the main determinant of hypertrophy, but the fact that the strength effects are similar is surprising, since generally training intensity (the percentage of your 1rm you’re training with) is an important determinant of strength gains. More on that a bit later.

It’s also worth pointing out that the BFR meta-analysis was just looking at studies that solely utilized BFR training, not BFR in addition to heavier, conventional training. I’m going to assume that most people reading this article are also lifting heavy stuff, and aren’t planning to use low-load BFR training for the entirety of their training plan, with perhaps the exception of when you’re rehabbing an injury. More on that later as well.

There are five studies worth digging into that had well-trained subjects and combined BFR training with heavy resistance training.

The first is a glorious study, because the muscle being trained was the biceps. That also makes it the least relevant for people primarily concerned with getting strong, but I’m sure that if you look deep down into your soul, you’ll be able to admit to yourself that getting jacked arms is a worthy training goal, and that they are a great compliment to a huge squat or deadlift.

Just tell me with a straight face that you don’t want to look like this.

The researchers split the subjects – college-aged men, with at least one year of lifting experience – into two groups. One group did curls with BFR for 4 weeks (3 sets of 30 reps with 30% of their 1rm), followed by heavier curls for 4 weeks (3 sets of 15 with 60% of their 1rm). The other group did heavier curls for 4 weeks, followed by curls with BFR for 4 weeks.

Both groups gained the same amount of muscle over the 8 weeks of the study. They also gained the same amount of muscle during their BFR phase as their heavier training counterparts did; during the first four weeks, the people doing BFR curls gained as much muscle as the people doing conventional curls, and during the last 4 weeks when they changed training protocols, the people doing BFR curls (who did heavier curls for the first 4 weeks), again, gained the same amount of muscle as the people who did heavier curls (the people who did BFR curls for the first 4 weeks).

Over the course of 7 weeks of offseason training for Division IAA football, he split the players into four groups:

One group just followed the standard high-intensity off-season training program for football.

One group did the same high-intensity training program, with additional sets of squat and bench with 20% of their 1rm (1 set of 30 and 2 sets of 20) without BFR.

One group did the same high-intensity training program, with additional sets of squat and bench with 20% of their 1rm utilizing BFR.

One group basically just did accessory work, along with the light squats and benches with BFR.

Over the course of the study, the athletes’ arms and legs got bigger, and their chests didn’t, but there were no significant differences in hypertrophy between the training protocols.

When looking at strength, however, the group doing high-intensity training combined with low-intensity BFR had the largest increases in the squat. Their squats increased ~25kg over 7 weeks, vs. ~14kg for the group only doing high intensity training, and the group doing high intensity training plus low-load training without BFR. The group doing high-intensity training combined with low-intensity BFR also had the largest increases on bench, but the difference wasn’t significant (~8.5kg vs. ~7kg for the other two groups doing high intensity training).

Also note that these were pretty strong dudes to begin with. The average squat at the start of the study was around 200kg.

It’s also interesting to note that it seems like the stimulus from the BFR training is what drove the larger strength increase. My knee-jerk reaction was that the additional training volume was what made the difference, but the group doing the light squats without BFR, in spite of also having significantly higher training volume than the group only doing high-intensity training, gained the same amount of strength over the course of the study.

The researchers split the subjects (Division 1 football players) into two groups. Both groups continued their normal off-season strength training program. In addition to their normal high-intensity training, one group did one set of 30 reps, and 3 sets of 20 reps with 20% of their 1rm squat and bench with BFR, and the other group did the same sets and reps without BFR.

The group using BFR gained more strength in the squat and bench press than the group doing the same sets and reps with the same relative load without BFR. In addition, the BFR group’s chest circumferences increased more (~3.1 cm vs. 1.5cm).

They were split into two groups. The first group trained for 3 weeks without BFR, then for 3 weeks with BFR, and the second group followed the opposite pattern.

They trained three times per week, doing 5 sets of 5 with 70% of their 1rm for squat, bench press, and pull-ups each day. The cuffs to restrict blood flow were only applied to the legs (even for pull-ups and bench press) and were removed between sets.

During their time doing BFR training, the athletes added an average of 5.4kg to their bench, and 7.8kg to their squat. During their time without BFR, the athletes added an average of 3.3kg to their bench, and 4.3kg to their squat.

This study was interesting for a couple reasons. For starters, even though the cuffs were only applied to the legs, even during upper body exercises, the BFR group still had a larger increase in bench strength, suggesting that BFR may have systemic effects in addition to the local effects in the muscles with restricted blood flow. Additionally, they were using relatively high loads (70% of their max) – not the low loads typically used in BFR studies.

His study also combined high intensity training and low-load BFR training.

One group trained exclusively with loads in excess of 70% of their 1rm and no BFR.

The other group did 38% of their training with loads in excess of 70% of their 1rm with no BFR, and 62% of their training with 30% of their 1rm and BFR, for one set of 30, and three sets of 15.

Training volume (total weight lifted) was roughly equated.

Over the course of the study, both groups’ bench press, leg press, biceps cross sectional area, and thigh circumferences increased, with no significant differences between groups. These were already relatively strong guys on the outset as well – they were benching around 220-245lbs, and leg pressing around 800lbs.

So, on the whole, we can take a few things away from these five studies that combined conventional high-intensity training and low-load BFR training and pretty well-trained athletes.

Low-load BFR training works about as well as heavier training for building muscle (Lowery’s study), though the effects of combining the two may not be additive for hypertrophy. Leubbers’ study showed that adding BFR training to high-intensity training didn’t increase hypertrophy, but Yamanaka’s did.

It appears that BFR training doesn’t just affect the muscles with venous blood flow occluded. Both Yamanaka’s study (increased chest growth when the cuffs were applied to the arms) and Cook’s study (larger increases in bench press, even though only leg blood flow was restricted) demonstrated increases in either strength or hypertrophy in muscles other than those below where the cuffs were applied.

The most notable effect seems to be an increase in strength. Leubbers’ study showed a larger increase in the squat, Yamanaka’s study showed a larger increase in both squat and bench press, Cook’s study showed a larger increase in both squat and bench press, and O’halloran’s Thesis showed that substituting a sizable chunk of high-intensity training for low-load BFR led to the same increases in strength.

The effects on strength are the most surprising. You’d expect (or at least, I’d expect) there to be a bigger difference in hypertrophy, but apparently the mega-pump lies to you.

When you think through it, though, it makes sense. Plenty of things make muscle grow; tension, volume, metabolite accumulation, muscle damage, etc. With low-load BFR, tension is lower, metabolite accumulation is high, but not any higher than conventional training for 10+ reps, and there’s very, very little muscle damage that takes place. It gives you a solid growth stimulus, but nothing that you can’t also get from just picking up heavy stuff, and when you add it to a program that revolves around picking up heavy stuff, it doesn’t seem to offer any additional hypertrophy benefits.

However, strength is another beast entirely. Strength is partially dependent on structural factors (how much muscle you have), and partially dependent on neural factors (how well you can activate those muscles). Remember, low-load BFR causes roughly the same amount of muscle activation as much heavier, conventional training.

BFR training has proven to be pretty disappointing for people with the sole goal of building muscle, since notable increases in muscle growth on top of heavier training haven’t really manifested themselves (with the exception of additional chest growth in Yamanaka’s study).

However, low-load BFR training is basically the holy grail for strength athletes, at least as far as accessory work goes.

When you add it to heavy training, it makes you stronger than heavy training alone. It’s not just a matter of getting stronger from adding extra training volume because it beats out low-load training without BFR.

It’s incredibly easy to recover from since it causes essentially no muscle damage. (note: you may very well get sore the first couple of times you do it, simply due to novelty; this should go away pretty quickly, though)

Because it also causes high muscle activation, it also aids in the neural side of strength development. Its effects are very similar to heavy training, and O’halloran even showed that you can replace a hefty amount of heavy training with low-load BFRs and get the same increases in strength.

You can almost think of it as “free” volume. You get all the upside of lifting heavy, but it’s way easier to recover from. You can add low-load BFR to your current training program to get stronger, faster without compromising recovery. Or, if you’re having issues with recovery, you can sub out some (not all) of your heavy training for low-load BFR and get the same strength increases without taxing your ability to recover to nearly the same degree.

Other Stuff Worth Noting

BFR without strength training speeds up recovery from training. One study showed that 2 sets of 3 minutes of BFR for the legs immediately after a training session significantly sped up recovery and enhanced subsequent performance for power-related tests.

BFR can also decrease muscle atrophy when you’re injured, and speed up the recovery of strength when you can get back to training. In one study, BFR (multiple sets of 5 minutes of occlusion, without exercise) significantly decreased muscle atrophy of the quads and hamstrings during the post-operative period following ACL reconstruction. In another, low-load BFR training helped people get muscle and strength back faster than training without BFR during the reconditioning phase following ACL reconstruction. Low-load BFR training can be a godsend to people dealing with or recovering from injuries. BFR without training can keep you from losing as much muscle if you’re so jacked up you can’t do anything (of course, consult with a physical therapist first), and low-load BFR training can help you maintain muscle and strength if you have aches and pains you need to train around. If you want to read more about how to progress from totally-jacked-up to picking-up-heavy-stuff-again, I’d strongly recommend this review.

Keep in mind, I’m not recommending low-load BFR as the sole focus of your training plan. You should still be picking up heavy stuff (of course, since you’re reading Strengtheory, I doubt I have to tell you that). One study showed that low-load BFR doesn’t affect tendons to the same degree heavy training does.

Interestingly, it seems that the additive increase in strength only applies to well-trained athletes. One study on untrained folks found that adding low-intensity BFR training to heavier training didn’t increase strength gains. It could be that untrained people are already getting all the strength benefits they could possibly get just from picking up heavy stuff, but that more well-trained people have that capacity for greater increases in strength that don’t manifest themselves because further increases in heavy training would compromise their ability to recover (since their training is already inherently more stressful). That seems plausible enough to me.

People get leery of BFR because cutting off blood flow just seems like it would be dangerous. However, rates of adverse effects are exceptionally low, even in diseased and at-risk populations. You can completely cut off blood flow to a limb for over an hour without any long-term risks, and with BFR training, you’re still allowing arterial blood flow, so you could likely occlude venous blood flow for even longer (though I wouldn’t recommend it).

The thinner the device for cutting off venous blood flow, the better off you are. With thicker wraps, you run a greater risk of cutting off arterial blood flow. I generally use the resistance bands you can find in most gyms that some middle-aged women use for biceps curls. I get weird looks when I raid the BodyPump room in the middle of a class, but #yolo. Knee wraps can do the job as well, but bands are a better option if they’re available to you.

Bro-tip: BFR work seems to work best, in my experience, when added in for a 4-8 week block, then replaced with more conventional accessory work for the next 4-8 week block.

Implementation

Pick up heavy stuff as you generally would. You don’t need to really change your program to add low-load BFR since it’s exceptionally easy to recover from.

After your heavy sets, do 3-4 sets of 15-40 reps with 20-30% of your max with BFR, resting about 30 seconds between sets. Whether you leave the wraps on between sets or take them off is up to you, but leaving them on seems to be better for muscle activation, and they’re annoying to take off and put back on between sets anyways. This works really well for squat and bench (or you could do leg press and DB press after your squat and bench work, if you prefer). Whether it helps the deadlift or not hasn’t been examined in the literature, and anecdotally, it doesn’t seem to help out your hammies as much as your quads.

Though not required, I’d strongly recommend you also bust out a sweet superset or five for your arms. Who cares if science says it won’t make your arms grow any faster than regular curls and triceps extensions? You get the same hypertrophy effect, but you get it by way of stupidly awesome pumps, which is a benefit in and of itself.

Alternately, if you’re having issues recovering from your training, you can sub out one or two heavy sets for 2-3 sets of low-load BFR. This is particularly useful for short stints when you know beforehand that recovery will be compromised (if you know you have a deadline coming up that’ll stress you out and decrease how much you can sleep, or something of that sort).

If this is a subject that interests you, I’d strongly recommend you check out these three reviews as well (one, two, three).

This was a snippet from the Second Edition of the Art and Science of Lifting that I’m working along on right now. If you already have the First Edition, the Second Edition will be free for you when it comes out!

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About Greg Nuckols

Greg Nuckols has over a decade of experience under the bar, a BS in Exercise and Sports Science, and a Master's in Exercise Physiology. He’s held 3 all-time world records in powerlifting in the 220 and 242 classes.

He’s trained hundreds of athletes and regular folks, both online and in-person. He’s written for many of the major magazines and websites in the fitness industry, including Men’s Health, Men’s Fitness, Muscle & Fitness, Bodybuilding.com, T-Nation, and Schwarzenegger.com. Furthermore, he’s had the opportunity to work with and learn from numerous record holders, champion athletes, and collegiate and professional strength and conditioning coaches through his previous job as Chief Content Director for Juggernaut Training Systems and current full-time work here on Stronger By Science.

His passions are making complex information easily understandable for athletes, coaches, and fitness enthusiasts, helping people reach their strength and fitness goals, and drinking great beer.